As a form of new generation broad band mobile device, a cellular system where a group of narrow cell base stations are connected by wireless multihop relay is studied. In this system, some base stations called core nodes are connected to the backbone network by lines and other nodes are connected to the backbone network by wireless multihop relay via a core node.
Such a wireless relay network is usually called a wireless backhaul. The stable operation and the enlargement depend of the wireless backhaul on the realization of an excellent wireless multihop relay protocol. The routing protocol of a wireless backhaul is characterized in its metric and algorithm and algorithm varies depending on the definition of the metric. The metrics proposed so far includes hop count and the quality of wireless link between nodes, for example. That is, ETX (Expected Transmission Count) metric, RTT (Per-hop Round Trip Time) metric, WCETT (Weighted Cumulative Expected Transmission) metric, and so on. The commonly used conventional algorithms include Bellman-Ford algorithm, Dijkstra algorithm, and so on.
In addition, the present inventors proposed routing methods (referred to as “conventional minimum path loss routing” below) where path loss is adopted as the metric (Patent Documents 1 through 3 and Non-Patent Document 1.) The conventional minimum path loss routing makes a relay route such that the path loss from each slave node to a core node is minimum using Bellman-Ford algorithm by calculating the path loss based on the reception power between nodes (RSSI, Received Signal Strength Indicator) as the metric. Referring to FIG. 8, the conventional minimum path loss routing will be described concretely. FIG. 8 shows a flowchart indicating the behavior of the slave node in the conventional path loss routing. When a core node broadcasts a routing packet of metric 0 and a slave node receives the routing packet (step STSP1), the path loss is calculated based on the RSSI at reception and a new metric is calculated by adding the path loss and an accumulated metric (indicating the sum of path losses from the transmission source node of the received packet to the core node) included in the received packet (step STSP2.) If this new metric is smaller than an accumulated metric held by the own node (step STSP3), a route is updated and the routing packet including the new metric is broadcasted to neighbor nodes (step STSP4.) In the step STSP3, if the new metric is not smaller, the route will not be updated. By repeating the processing above, a route is made. And if a predetermined time is passed without receiving any routing packet (step STSP5), a node registration packet is transmitted (step STSP6), and the processing is quitted. Finally, a tree-type route where a core node plays a central role is made. Because the path loss is adopted as a metric in the minimum path loss routing, the made relay route as a whole is tolerant of interference. Thus, the excellent and highly efficient transmission can be expected.
In addition, many methods are already proposed as a routing protocol for wireless multihop relay. And the standardization of ad-hoc-type wireless backhaul is being promoted by MANET (Mobile Ad-hoc Networks) WG of IETF (Internet Engineering Task Force.)